1. Field of the Invention
This invention relates to a CVD (chemical vapor deposition) device equipped with a self-cleaning device. In particular, the invention relates to a device that cleans the inside of a deposition chamber using remotely generated active species.
2. Description of the Related Art
CVD devices have been conventionally used to form insulation films such as silicon oxide, silicon nitride, amorphous carbon or polymer containing benzene ring, conductor films such as tungsten silicide, titanium nitrite or aluminum alloy and high-dielectric films containing PZT (PbZr1xe2x88x92xTixO3) or BST (BaxSr1xe2x88x92xTiO3) on silicon a substrate or glass substrate.
To form these films, reaction gas with various compositions or a second reaction gas is supplied within a deposition chamber. These gases cause a chemical reaction by receiving plasma energy and a desired thin film is formed on a semiconductor substrate. Within a reaction chamber, films that are generated similarly by chemical reaction adhere to its inner wall and the surface of a wafer support. These adhesive substances are accumulated gradually as film formation is repeated. Then, disengaging from the inner wall and the surface of the support, these adhesive substances sometimes float within the reaction chamber. This causes impurity contamination that leads to defects in manufactured semiconductor circuits.
To remove contaminants adhering to the inner wall of the reaction chamber, in situ cleaning that cleans the inside while the reaction chamber is in operation is effective. This method is to remove adhesive substances by bringing cleaning gas, which is selected according to the type of adhesive substances, into the reaction chamber to decompose the adhesive substances into gaseous materials. For example, if silicon oxide or silicon nitride, tungsten or its nitride or silicide adheres, CF4, C2F6, C3F8 or NF3 is used as cleaning gas. In this case, active species (fluorine radical) of fluorine atoms or fluorine-containing active species decomposes the substances adhering to the inner wall of the reaction chamber and impurities can be removed in the gas phase.
In the case of a plasma CVD device, because a plasma excitation device used for film formation is also used for activation of cleaning gas, large ion bombardment is caused between electrodes by high radio frequency (RF) power applied to the cleaning gas. As a result, the surface of electrodes is damaged; a surface layer comes off to cause impurity contamination. It becomes necessary to replace damaged parts frequently, which increases operation cost.
To solve these shortcomings caused by ion bombardment, remote plasma cleaning was developed. In U.S. Pat. No. 5,788,778, issued Aug. 4, 1998, and U.S. Pat. No. 5,844,195, issued Dec. 1, 1998, which are herein incorporated by reference, a method is disclosed in which NF3 is used as a cleaning gas and plasma excitation that activates NF3 is performed using microwaves in the second plasma discharge chamber, which is different and is separated from the reaction chamber. According to this method, flow-controlled NF3 is brought into the second plasma discharge chamber, it is dissociated and activated by 2.45 GHz microwaves supplied to the plasma discharge chamber from a microwave oscillator through a waveguide, and fluorine active species are generated. At this time, to achieve microwave plasma discharge efficiently, a valve is provided between the second plasma reaction chamber and the reaction chamber to regulate pressure and the second plasma reaction chamber is maintained at a designated pressure. Generated fluorine active species are brought into the deposition chamber through a conduit, and it decomposes and removes adhesive substances on the inner wall of the reaction chamber.
In U.S. Pat. No. 5,788,799, issued Aug. 4, 1998, which is herein incorporated by reference, it is disclosed that for the conduit that brings fluorine active species into the reaction chamber, aluminum is preferable to stainless steel and that Teflon materials such as polytetrafluoroethylene (PTFE) are the most preferable.
In U.S. Pat. No. 5,844,195, issued Dec. 1, 1998, which is herein incorporated by reference, along with activation of cleaning gas in the second plasma discharge chamber, it is disclosed that cleaning gas is supplementarily activated further using radio-frequency plus true electric discharge in the reaction chamber and that a filter is provided between the second plasma discharge chamber and the reaction chamber to remove undesirable particles. This technology is also reflected in the teachings of U.S. Pat. No. 5,788,778.
While the above-mentioned remote plasma cleaning methods alleviated the problems caused by ion bombardment, there remains a need for improvement in these methods.
Among various embodiments of the present invention, an embodiment is to provide a remote plasma discharge chamber comprising materials that are resistant to damage, and at the same time, to provide reaction chamber cleaning without ion bombardment.
Another embodiment of this invention is to provide a CVD device in which plasma ignition at the remote plasma discharge chamber is easy and reliable.
Yet another embodiment of this invention is to provide a CVD device that quickly exhausts residual gas within piping after supply of activation cleaning gas is stopped.
Further, another embodiment of this invention is to provide a plasma CVD device that supplies cleaning gas to the reaction chamber by maintaining the amount of fluorine species that is activated in the remote plasma discharge chamber.
That is, a plasma CVD device according to this invention includes the following embodiments:
The CVD device of the preferred embodiments comprises a reaction chamber, a remote plasma discharge chamber that is provided remotely from the reaction chamber, and piping that links the reaction chamber with the remote plasma discharge chamber. The remote plasma discharge chamber activates cleaning gas by plasma discharge energy. The activated cleaning gas is brought into the inside of the reaction chamber through the piping and changes solid substances, which adhere to the inside of the reaction chamber as a consequence of film formation, to gaseous substances, thereby cleaning the inside of the reaction chamber. The device is characterized by at least one of the following:
(a) the remote plasma discharge chamber generates active species using radio-frequency oscillating output energy of a preselected frequency;
(b) the piping is made of materials that are not corroded by the active species; or
(c) the piping is provided with a through-flow type valve.
According to one embodiment, the device further comprises a support provided within the reaction chamber, which supports an object to be or being processed, and a gas-emitting plate provided at a position facing the support within the reaction chamber. The plate uniformly supplies reaction gas to the object being processed to form a film onto the object being processed, wherein the activated cleaning gas is supplied through piping into the reaction chamber from holes provided through the gas-emitting plate.
With regard to (a) above, in an embodiment, the preselected frequency is 300 kHz-500 kHz and the active species is a fluorine activated species. With regard to (b) above, in an embodiment, the inside surface of the piping is made of fluorine-passivated stainless steel, aluminum or aluminum alloy. With regard to (c) above, in an embodiment, the size of the opening of the valve, when fully opened, is substantially equal to the inner diameter of the piping, and the valve does not have projections, when fully opened, with respect to the inner surface of the piping. Namely, the valve has an opening, when fully opened, such that the pressure drop across the valve is preferably less than about 0.25 Torr (or less than about 5% of the inlet pressure), more preferably less than about 0.1 Torr (or less than about 1% of the inlet pressure), and most preferably substantially no pressure loss is caused. In the above, the piping is preferably straight in the vicinity of the valve. Most preferably, all three of these features are combined to produce an efficient, self-cleaning CVD reactor.
As a result of (a), the following advantages can be realized: use of radio-frequency (e.g., 400 kHz) oscillating output allows manufacturing the remote plasma discharge chamber from anodized aluminum alloy, for example. Thus, it is unnecessary to use sapphire or quartz, which are required when conventional microwave output is used. Risk of damage during processing and problems of fluorine active species consumption are thereby reduced. In addition, damage to electrodes by ion bombardment at the time of cleaning and deterioration of electrode surfaces can successfully be prevented. Moreover, complex tuning circuits are unnecessary and miniaturization of the remote plasma discharge chamber and lower cost can be realized. Furthermore, a phenomenon wherein powdered aluminum fluoride adsorbs onto the electrode surface is reduced or eliminated and device downtime due to device maintenance can be considerably shortened. As a result, productivity is improved.
As a result of (b), the following advantages can be realized: use of materials inert to fluorine active species for internal surfaces of the piping and the valve, instead of resin materials such as PFA, adsorption of fluorine active species or fluoride gas onto the internal surface of the piping or the valve can be eliminated. Thus, the occurrence of fluorine active species or fluoride gas being released from the internal surface of the piping and the valve after cleaning is completed and remaining within the remote plasma discharge chamber is reduced or eliminated. Accordingly, the occurrence of plasma ignition failure can be controlled. Moreover, when supply of fluorine-containing gas is stopped, fluorine active species is promptly discharged from the piping and the remote plasma discharge chamber. Reduction of fluorine adsorption also increases the amount of fluorine active species brought into the reaction chamber, thereby maintaining the activity of active species and improving cleaning efficiency.
As a result of (c), the following advantages can be realized: use of rectilinear piping with a large internal diameter and a valve that does not restrict flow between the remote plasma discharge chamber and the reaction chamber, deactivation (recombination) of fluorine active species is reduced, due to reduced collisions with the piping surface and structure within the valve. Accordingly, applying radio frequency power of less than 3,000 W to the remote plasma discharge chamber, high-speed cleaning at over 2 micron/min becomes possible. Furthermore, reduced collisions also minimizes thermal energy generated when fluorine active species is deactivated, thus reducing overheating of the piping and the valve. Heat damage to O-rings and other components, and consequent generation of particles is also reduced or eliminated. The frequency with which damaged parts are replaced thus decreases, and operating costs of the device can be decreased while at the same time increasing productivity of the device.
The skilled artisan will readily appreciate in view of the present disclosure that, while each of features (a), (b), and (c) are advantageous in and of themselves, combining two or all of (a), (b) and (c) will synergistically enhance the advantageous effects.